Conventionally, as disclosed in JP 2008-186279 A, a display system includes a display unit and a touchpad. In the display system disclosed in JP 2008-186279 A, the display unit displays icons, each of which is linked to a corresponding predetermined function, on a screen panel, and the touchpad is manipulated by a user to select a target icon displayed on the display unit. Further, JP 2000-214977 A (corresponding to U.S. Pat. No. 6,538,670 B1) discloses a display system including a display unit and keys. The display unit displays display windows on a screen panel of the display unit, and each key is used to select a corresponding display window displayed on the screen panel. An arrangement of the keys corresponds to an arrangement of the display windows. When one of the keys is manipulated by a user, a corresponding display window is selected and is displayed on the screen panel in an enlarged manner.
Recently, a screen panel of a display system tends to turn into a high-definition screen panel and a size of the screen panel tends to increase. When the display unit of the display system disclosed in JP 2008-186279 A displays an image on a high-definition screen panel, a size of each icon displayed on the screen panel will be reduced. For example, the icons may include button images. When a size of the screen panel is enlarged and a size of the touchpad remains the same, a ratio of the size of the touchpad to the size of the screen panel reduces. Thus, when the user manipulates the touchpad to select a target icon displayed on the screen panel, it is difficult for the user to accurately manipulate the touchpad to select the target icon displayed on the screen panel. Thus, a manipulation time for selecting the target icon displayed on the screen panel increases.
In view of the foregoing difficulties in JP 2008-186279 A, the inventor of the present disclosure thought of adding keys disclosed in JP 2000-214977 A for selecting corresponding display windows to the display system disclosed in JP 2008-186279 A. In a display system which has a combined structure of JP 2008-186279 A and JP 2000-214977 A, each display window is selected by manipulating a corresponding key. Further, an icon is selected by manipulating of the touchpad. With this configuration, a manipulation switch becomes complicated. Specifically, when the user switches from a manipulation to the key to select the display window to a manipulation to the touchpad to select the target icon, the user needs to change a manipulation position from the keys to the touchpad. Thus, it is difficult for the user to reduce a manipulation time for selecting the target icon displayed on the screen panel of the display system, which has the combined structure of JP 2008-186279 A and JP 2000-214977 A.